1. Field of the Invention
The present invention relates to an optical circuit system (for example, an optical circuit, optical LSI, optical circuit substrate, backplane optical circuit) which can produce an optical signal for propagation along an optical circuit composed mainly of an optical waveguide and optical fiber, more particularly which can produce an optical signal with a small fluctuation in intensity by a plurality of electrical elements without the use of separate electro-optic conversion elements and to components of the same (for example, optical tabs, optical switches, optical couplers, waveguide optical amplifiers, waveguide optical lasers, and optical couplers).
The optical circuit system and components according to the present invention are suitable for use in optical information fields such as optical communications and optical interconnection.
2. Description of Related Art
Optical circuits, as is well known in the art, play an important role in various optical information processing systems such as optical exchanges in optical communication. We have proposed various systems regarding optical circuits for optical interconnections wherein we form optical circuits by coupling IC's, multichip modules, boards, etc. by optical waveguides in optical circuits using optical waveguides and optical fibers and transmit signals over the same. According to these proposals, the optical circuit is primarily formed by optical waveguides. In an optical circuit comprised primarily of optical waveguides, however, there is the problem of attenuation of the intensity of the signal light along with the propagation and transmission of light.
Further, proposals have been made of various systems for generating optical signals from electrical signals. For example, a proposal has been made of the method of guiding non-signal light generated at a light source through an optical waveguide and generating signal light having intensity modulation by a voltage-controlled type optical branching filter formed by an electro-optic material etc. In these methods, however, when generating a plurality of signal lights from a single waveguide, there is the problem of the difficulty in obtaining signal light with a fixed intensity.
On the other hand, as an element for amplifying the attenuating signal light, in the field of optical communications, study has been made of optical amplification fibers using optical fibers. While these are effective as elements for amplifying the signal light propagated through an optical fiber, there is the problem that they are not suitable in terms of integration or compatibility as elements for amplifying the signal light propagated through an optical waveguide.
On the other hand, waveguide optical amplifiers and waveguide lasers are applied for the above-mentioned optical circuits and are promising in themselves as the important components in various types of optical systems.
That is, optical fiber amplifiers comprising optical fibers doped with rare earth ions are used for long distance optical communications. To use waveguides in the long distance optical communications and to make optical systems more compact is effective for reduction of the size of optical systems. In the case of a waveguide, however, since the optical path becomes shorter, it becomes necessary to increase the amount of doping depending on the shortness of the path. Until now, attempts have been made to realize a waveguide amplifier of a polymer by doping the polymer with molecules containing a rare earth element or with rare earth ions in large amounts, but there were problems of reabsorption of the light and of light extinction due to the large amount of doping of rare earth-containing molecules or rare earth ions. Similar problems also arose in a glass-type waveguide.
On the other hand, along with the higher speeds and greater miniaturization of LSI's, the problem of wiring delay and heat generation have arisen. In view of this, numerous attempts have been made to introduce optical wiring for the wiring inside the LSI's, between LSI's, and between boards (MCM's). In a system where a large number of light emitting elements are made in a conventional chip and signals are sent by turning these on and off, there have been various difficult problems such as the need to fabricate the micro LD's on the Si wafer by a heteroepitaxy method, to finely adjust the position of the optical couplers, etc. As opposed to this, there is a method of mounting LD's and PD's in a hybrid fashion, but also in this case, the problem has remained of a difficulty in improving the efficiency of optical couplers such as the need for fine positional adjustment.
Furthermore, general problems of optical wiring include the fact that the amount of light reaching the light receiving element ends up changing depending on the number of fanouts or that there is no simple method of formation of waveguides in the longitudinal direction, and therefore, there are the problems that, when introducing light into the substrate, the majority is introduced from the lateral direction or the degree of freedom of introduction of light is small and when connecting a spatial beam (i.e., a beam propagating through space), there is the problem that there is no effective means of beam control. It should be noted that a hologram would be effective, but until now, holograms have been flat, and therefore, there was the problem that noise became terrible, when trying to control a large number of beams.
On the other hand, optical switches play an important role in various optical systems such as optical interconnections in computers and optical exchanges. As such optical switches, there have been known directional coupler systems in the past and intersection-type full-reflection type optical switches. Directional couplers, however, are sensitive to fluctuations in dimensions and temperature and in particular are difficult to use for matrix optical switches comprised of optical circuit substrates with large temperature fluctuations or large numbers of optical switches integrated together. Further, there is the problem that it is difficult to operate them with multimode waveguides. On the other hand, intersection-type full reflection type optical switches have the problem of residual crosstalk at the cross portion. Also, these two types of optical switches are limited in function to switching inside waveguides and therefore there was the problem that it was not possible to the switch to space.